1. Field of the Invention
This invention relates to a controller for an alternating current (AC) generator in vehicles that can restrict the change of engine rotating speeds and compensate the shock against a bearing fixed on the shaft of the engine or the AC generator when an electric load is switched on.
2. Description of the Prior Art
FIG. 1 illustrates a circuit diagram of the conventional controller for AC generator in vehicles, wherein numeral 1 shows an AC generator comprised of an armature coil 101 and a field coil 102 to be driven by an engine mounted on a vehicle, which is not shown in the diagram.
And numeral 2 shows a rectifier having a main output terminal 201, an auxiliary output terminal 202, and a ground terminal 203 so as to rectify in full wave the AC output of the generator 1. The main output terminal 201 is to supply a main output; and then the auxiliary output terminal 202 is to energize the field coil 102 and add a rectified output voltage of the generator 1 to a voltage regulator 3, which will be described later.
The voltage regulator 3 that controls the output voltage of the generator 1 to a predetermined value comprises the following parts: a serial circuit of resistors 301 and 302 is connected between the auxiliary output terminal 202 of the rectifier 2 and the ground, and the resistors 301 and 302 are used for dividing the output voltage of the auxiliary output terminal 202.
A connecting point of resistors 301 and 302 is connected to the base of a transistor 304 through a zener diode 303, and the transistor 304 is turned on or off according to the conductive or non-conductive condition of the zener diode 303.
An emitter of the transistor 304 is connected to the ground and a collector of the transistor 304 is connected to the base of an output transistor 305. The collector of the transistor 304 is connected to the auxiliary output terminal 202 through a base resistance 306. In the output transistor 305, an emitter is grounded and a collector is not only connected to the auxiliary output terminal 202 through a diode 307 but connected to the terminal 202 through the field coil 102.
The output transistor 305 is controlled to be conductive or non-conductive by the transistor 304 so as to regulate a field current of the field coil 102.
The diode 307 is connected in parallel with the field coil 102, absorbing a surge current generated by the connection and disconnection of the field coil 102.
As for a battery 4, a minus terminal is grounded, and a plus terminal is connected to the auxiliary output terminal 202 through a key switch 7 and an indication lamp 8.
The main output terminal 201 of the rectifier 2 is not only connected to the plus terminal of the battery 4, but grounded through a load switch 6 and an electric load 5.
FIG. 2 is a characteristic diagram showing the operational waveform of each part of the conventional controller. Every operating condition is illustrated in the figure, from a small electric load until the load that should have the maximum output power of the AC generator 1 is connected. The axis of abscissa represents time.
FIG. 2(a) shows operational waveforms made by the connection and disconnection of the output transistor 305 of the voltage regulator 3. FIG. 2(b) is a field current waveform of the AC generator 1, FIG. 2(c) an output current waveform of the AC generator 1, and FIG. 2(d) a driving torque waveform of the AC generator 1; point (A) indicates a time when the electric load that requires the maximum output is switched on.
Now, the operation of the conventional device is described referring to FIG. 1. When the key switch 7 is closed on starting the engine, an initial exciting current flows through the key switch 7, from the battery 4 to the indication lamp 8 and the field coil 102. Therefore, the AC generator 1 is ready for generating power, but the indication lamp 8 is lighted on to indicate that the electric power is not being generated.
When the engine is started, the AC generator 1 begins to supply an electric power, increasing the voltage of the auxiliary output terminal 202 of the rectifier 2, and, at the same time, decreasing a potential difference across the indication lamp 8. This difference, at last, becomes zero, which switches off the indication lamp 8 so as to show the electric power being generated normally by the AC generator 1.
The voltage regulator 3 detects the output voltage of the auxiliary output terminal 202 of the rectifier 2 by using the zener diode 303 and the resistances 301 and 302 for voltage dividing. Thus, when the output voltage of the auxiliary output terminal 202 exceeds the value preset by the resistances 301 and 302 and zener diode 303, the diode 303 becomes conductive so as to turn on the transistor 304.
When, on the other hand, the output voltage of the auxiliary output terminal 202 is equal to or less than the above preset value, the zener diode 303 becomes non-conductive; thus, the transistor 304 is turned off.
As, in this manner, the output transistor 305 is turned on or off in accordance with the connection or disconnection of the transistor 304, the field current is controlled to flow into or be cut off from the field coil 102. Therefore, the output voltage of the AC generator 1 is regulated to the predetermined value.
In the conventional controller constructed as above, when the AC generator 1 is being operated in a condition of a small load and then the electric load 5 is switched on by the load switch 6 so that the maximum output is required as shown in FIG. 2 shown as the point (A)), the output voltage of the AC generator 1 becomes less than the predetermined value so that the output transistor 305 of the voltage regulator 3 is turned on instead of the preceding on and off condition.
Therefore, the field current of the AC generator 1 increases according to the time constant of the field coil 102 (ca. 100 msec.) until it reaches the maximum field current (FIG. 2(b)). Then the output current of the AC generator 1 reaches its maximum value by its operation proportional to the field current (FIG. 2(c)), and therefore the driving torque reaches its maximum value under the present condition (FIG. 2(d)). That is, when the electric load 5 is switched on by using the load switch 6, it increases the field current, in proportion to which the output current and the driving torque increase. The increasing rate is determined by the time constant that is characteristic of the field coil 102, 100 msec. or less in general.
Therefore, the driving torque of generator 1 increases within an interval about 100 msec. so that the load of the engine goes up suddenly to drive the AC generator 1; this leads to an unstable condition of the engine rotating speed. Moreover, as the engine and the AC generator 1 are connected by using a V belt or the like in general, a sudden change of the load will lead to slippage of the belt, generate creaking noises, and shorten its lifetime. Furthermore, the sudden change of the load adds the stress to the bearings of the engine driving shaft and the rotor of the AC generator 1, so we have a disadvantage which affects the lifetime of the bearings.
Since the controller of the conventional AC generator in vehicles is constructed as described above, there are the troubles that, when a large electric load is connected to the AC generator 1, a sudden change of the driving torque causes the engine rotating speed to become unstable, the V belt which connects the engine and the AC generator to slip and make noises, its lifetime to shorten, or affects the bearings mounted on the shafts of the engine and the AC generator.